The present invention relates to heat exchangers, and more particularly to a new and improved high effectiveness contour matching contact heat exchanger having substantially greater manufacturing and physical distortion tolerances than prior devices.
In the design and manufacture of heat exchangers, it is desirable to maximize heat transfer efficiency while keeping fabrication costs to a minimum. Depending upon the intended application, other factors such as size and weight may also be critical. Examples of the latter include heat management needs ranging from outer space applications (such as in the Space Shuttle, or extra-vehicular space life-support/mobility units) to undersea heat transfer needs, etc. Objectives include high heat transfer effectiveness, low pressure drop, and uniform temperature and flow distributions perpendicular to the fluid flow direction. Additionally, the heat exchanger should have a flexible core design to provide a contour matching capability which will compensate for manufacturing, assembly, and operational tolerance and distortion build-ups that could occur variously on the core and/or the surface of the external heat (or cold) source, and to provide a uniform thermal contact conductance between the core and external heat (or cold) sources under all operating conditions. Such contact can be provided by operating the heat exchanger core at a pressure level slightly higher than ambient, thereby contouring the flexible core to provide such contact.
To improve heat transfer efficiency, prior art heat exchangers have from time to time employed pins or studs extending from the exchanger plates into the fluid flow path. Such pins substantially increase the surface area contact between the plate/pin structure and the fluid flowing therepast. In addition, they interdict the fluid flow, forcing the fluid into a tortuous, non-stratified flow pattern which further enhances the heat transfer efficiency.
When each plate of the heat exchanger is allowed to operate substantially independently of the other(s), the pins usually contact only their own respective plates. If the pins are simply pushed against the opposite plate, they must then each be fabricated (as by machining or grinding) to very precise lengths--and even then expansion and contraction of the plates, for whatever reason, will open gaps of varying thicknesses at the ends of the pins. Such gaps can then seriously upset the fluid and heat flow patterns.
If, on the other hand, the pins are rigidly attached to both plates, as by welding, then subsequent stresses caused by thermal expansion and contraction of the plates will too often break the welds or plates or pins, with obviously undesirable results.
As suggested, the prior art fails to teach a solution to this problem. For example, U.S. Pat. No. 3,524,497 (Chu et al., issued Aug. 18, 1970) discloses a heat exchange apparatus employing cooling studs on one plate and turbulator studs on an opposite plate. No provision is made, however, for eliminating the gap between one end of the pin and the adjacent plate. Heat transfer efficiency is helped, however, through the use of alternate rows of studs and pins.
U.S. Pat. No. 3,828,850 (McMinn et al., issued Aug. 13, 1974) is directed to a high temperature material introduction apparatus which cools by the circulation of a coolant therein. Opposing walls are provided with alternating baffle plates to force the coolant to follow a tortuous path from one end of the apparatus to the other.
U.S. Pat. No. 3,796,255 (Streitz, issued Mar. 12, 1974) again utilizes alternating baffles on opposite plates to force the air flowing therethrough to follow a tortuous path.
A need thus remains for a strong, light weight, inexpensive, uncomplicated, versatile, and reliable heat exchanger having high heat transfer effectiveness, low pressure drop, uniform temperature and flow distributions, and particularly having a flexible core design which provides contour matching capabilities, which compensates for manufacturing, assembly, and operational tolerance and distortion build-ups, and which accordingly furnishes an essentially uniform thermal contact conductance between the core and external heat (or cold) sources under essentially all operating conditions.